1. Field of the Invention
The present invention relates generally to a disk cartridge with a write protect mechanism which prevents data stored on a magnetic disk from being erroneously erased from the disk and prevents new data from being erroneously written on the disk. More specifically, the invention relates to a high packing density disk cartridge with a write protect mechanism which has an identification recess for discriminating it from other types disk cartridge.
2. Description of the Background Art
Generally, disk cartridges have an erroneous erasure preventing mechanism or write protect mechanism in order to prevent the data stored on the magnetic disk from being erroneously erased from the disk and to prevent new data from being erroneously written on the disk. Such write protect, mechanisms are described in the U.S. Pat. Nos. 4,460,930 and 4,549,240.
Recent improvements of disk type storage media make the increase of packing density or track density thereof possible, so that disk cartridges having the same shape as that of conventional disk cartridges can have higher memory capacity. However, in cases where the shape of such a high packing density disk cartridge is the same as that of the conventional low packing density disk, when the high packing density disk cartridge is loaded into an adapted disk drive unit for low packing density disk cartridges, or when the low packing density disk cartridge is loaded into a disk drive unit adapted for high packing density disk cartridges, then the data stored on the magnetic disk tends to be destroyed due to the differences of recording characteristics, the width of track and so forth therebetween. In order to prevent such accidents, it is required to provide the write protect mechanism of the disk cartridge with an additional identification recess, by which the disk drive unit can discriminate a high packing density disk cartridge from other types disk cartridge so that it is not active when an incompatible type of cartridge is set thereon.
FIG. 1A illustrates a conventional 1 MB disk cartridge which is provided with a write protect mechanism. The write protect mechanism comprises an essentially rectangular first identification (ID) recess which is formed in the lower half at a location neighboring the rear-right corner thereof, and a manually operable switching member which engages the first ID recess so as to be movable between two positions, i.e. forward and backward positions. The disk drive unit for the 1 MB disk cartridge is provided with a first detecting switch SW1. In cases where the manually operable switching member is positioned at the rearward position of the first ID recess, the first detecting switch SW1 is designed to be received in the first ID recess when the disk cartridge is set in the disk drive unit. When the first detecting switch SW1 is depressed, it is turned ON, and when it is not depressed, i.e. when it is received in the first ID recess, it is OFF. In response to turning OFF of the first detecting switch, i.e. when the first detecting SW1 is received in the first ID recess at the forward position, write protect is performed. Therefore, in the cases where the manually operable switching member is positioned at the rearward position of the first ID recess, when the disk cartridge is set in the disk drive unit, it is possible to prevent the data stored on the magnetic disk from being erroneously erased from the disk and to prevent new data from being erroneously written on the disk, since the first detecting switch SW1 is not depressed and so remains OFF.
In the case of 2 MB disk cartridge shown in FIG. 2A, an essentially rectangular second ID recess is also provided in the lower half of the cassette casing at a location neighboring the rear-left corner. The second ID recess is arranged so that a straight line drawn between the forward position of the first ID recess and the position of the second ID recess is essentially parallel to the rear edge of the cassette casing. The disk drive unit for this 2 MB disk cartridge is provided with a second detecting switch SW2 besides the first detecting switch SW1. The second detecting switch SW2 is designed to be received in the second ID recess when the 2 MB disk cartridge is set on the disk drive unit. When the second detecting switch SW2 is depressed to be turned ON, it is detected that another type disk cartridge is set on the disk drive unit so that write protect is performed. Therefore, when a 1 MB disk cartridge is erroneously set on the disk drive unit for the 2 MB disk cartridge, it is possible to prevent the data stored on the magnetic disk from being erroneously erased from the disk and to prevent new data from being erroneously written on the disk, since the second detecting switch SW2 is depressed to become ON.
FIG. 3A illustrates another disk cartridge having 4 or 6 MB packing density, which will be referred to as "4/6 MB disk cartridge". In this 4/6 disk cartridge, the positions of first and second ID recesses are the reverse of their positions in the 2 MB disk cartridge. The positions of first and second detecting switches SW1 and SW2 are also the reverse of their positions in the 2 MB disk cartridge. That is, the first ID recess and the first detecting switch SW1 are arranged at a location neighboring the rear-left corner, and the second ID recess and the second detecting switch SW2 are arranged at a location neighboring the rear-right corner. Therefore, even if a 2 MB disk cartridge is erroneously set in the disk drive unit for the 4/6 MB disk cartridge, write protection is provided since the first detecting switch SW1 is not depressed and so remains OFF. The manually operable switching member is usually positioned at the forward position when the user wants to write the data on the magnetic disk. Therefore, even if a 1 MB disk cartridge is erroneously set on the disk drive unit for the 4/6 MB disk cartridge, write protection is provided since the second detecting switch SW2 is depressed to be turned ON. On the other hand, even if a 4/6 MB disk cartridge is erroneously set on the disk drive unit for the 1 or 2 disk cartridge, write protection is provided since the first detecting switch SW1 is not depressed and so remains OFF.
As set forth above, discrimination between 1, 2 and 4/6 disk cartridge has been achieved in the prior art.
Recently, disk cartridges having still higher packing density, such as 16 MB disk cartridges, have been developed. It is required to provide such 16 MB disk cartridges with another ID recess by which the set disk cartridge is identified as a 16 MB disk cartridge. If such an ID recess is formed in the cassette casing at a poorly selected position, the detecting switch corresponding to the ID recess can be not easily provided for the 16 MB disk cartridge.